Port mirroring is a technique used by a network switch to duplicate network traffic that pass through one switch port and send it simultaneously through another switch port. Port mirroring is commonly used for monitoring network traffic.
Port mirroring can be used in a Fibre Channel switch to configure a switch port to mirror the traffic passing in both directions between specific source and destination ports. The duplicate traffic is transmitted via a mirror port of the Fibre-Channel switch, which can be connected to a protocol analyzer to troubleshoot Fiber Channel end-to-end link communications.
Volume migration or volume replication are processes of copying a volume (source volume) from one storage system to another volume (destination volume) of a second storage system, where the two storage systems may be located at different locations and both are coupled to a Storage Area Network (SAN) network that includes Fibre-Channel switches or other switches.
A volume replication (also called mirroring) is a process where a target volume continuously and indefinitely synchronizes with the source volume, so that the target volume is regarded as a mirror of the source volume.
A volume migration is a finite process where once the content of the source volume is migrated to its new location, the source and destination volumes no longer synchronize with each other, the source volume may be superseded by the destination volume, and the path of input output (IO) flow coming from a host server is redirected from the source volume to the migrated (destination) volume, by changing the host volume configuration. The volume migration involves copying the entire content of the source volume to the destination volume (which is empty when the migration starts), which can take a significant amount of time. During this time, the host should be able to continue reading and writing the content of the volume while being migrated.
Some migration techniques redirect the host access paths to the destination volume when the migration starts. In this case, write requests are only implemented at the destination volume. The read requests are serviced from the destination volume if the requested blocks were already written to the destination volume and if not, the second storage system requests from the first storage system the not-yet-migrated blocks, which are then provided to the host by the destination storage system. In other migration techniques, the redirection of access requests towards the destination volume is done only when the migration is completed, so the first storage system is responsible for replying to all access requests until the migration is completed. In these scenarios, the first storage system should duplicate every write request it receives from the host during the migration process and send it to the destination storage system, as well as writing to the source volume.
The reliability of data stored in storage volume is paramount. Switch or network based traffic duplication processes are not reliable enough and cannot be used for copying volume content.